AC Servomotors - How sophisticated?

[Napier]

We're trying to figure out how AC servomotors work and have two competing mental pictures. We agree the motor has 3 phase stator windings and a PM rotor, and a resolver or encoder. We agree the drive reads the rotor position and generates an error signal that then dictates the current (or approximately the torque) the drive attempts to create. We further agree that the error signal may be interpreted in PID fashion, ie with proportional, integral and derivative gains.
One of us thinks the commutating logic in the drive tries to power the motor, observes the resulting rotation, and adapts its strategy accordingly. Therefore, if the three phases are connected incorrectly, the drive figures this out and changes which phase is energized next. For this reason, after wiring hundreds of servos, we have never had to rewire one to recover from what must be occasional wiring errors.
The other thinks the commutating logic in the drive is inflexible in this regard. Therefore, if the three phases are connected incorrectly, the system would just malfunction and be unable to respond correctly. All the drive logic can do is assume it is wired correctly and interpret any rotor position as an error relative to the desired position, and apply torque accordingly.
The debate started when we found this cryptic note in a servo's manual: "With the phases A, B and C connected to pins 2, 7 and 8, the rotation will be CCW facing the shaft." Is this just oddly worded, or is it meant to imply the motor would work properly in the other direction if you swapped two phases, like an induction motor?
We may try an experiment, if we have an extra system and convince ourselves it won't hurt anything. But that hasn't happened yet. Other manuals, circuit diagrams, and mfr's web sites have not settled the question.

[Dr. Lao]

I have no clue. So I asked my dad, who has 35 years experience as a electrical controls engineer working with drives and motors. He doesn't know either, but his guess is that the drive's logic is not smart enough. Tomarrow he is going out of town and will bring your question to one of the top drive techs in the country. I should be able to get your answer next time I talk to him.

[Napier]

Dang... and they say you can't get good information on the WEb...

Thanks - eagerly waiting...

[Balthisar]

At work, we use many types of drive amplifiers for old AC servo-motors (DC seems to be what the "new" stuff uses). On some of these, with old Num (I think Num) drive amps, reversing the phases just screws them up, i.e., they don't work, period. These are the "dumb" drive amps.

The newer AC drive-amps on newer machines are smarter. If the phases are backwards, the motor runs anyway, in the correct direction. I think these *could* be Num drive-amps, but I honestly don't remember.

[Napier]

Two bits of news that support the unsophisticated version of how servomotors work.
1) FWIW a sales rep for Kollmorgen (big servomotor maker) says the drives can't figure out what's wrong if you swap phase wires.
2) I tried a Kollmorgen Goldline XT servomotor yesterday. This motor has 3 phases and a resolver for feedback. I swapped phases A and B, and the motor did not rotate. Another motor next to it during the experiment, on which phases were left corectly wired, did rotate as expected.

[astro]

From the profusion search engine
http://www.worldservo.com/html/arc.htm

Investigating Servo Architectures- Pros and Cons

"The following discussion, to the best of our knowledge is the only public description of the subtle, yet substantial differences between servo control boards, various torque amplifiers, and the various architectures used in digital servo drives on the market today."

etc etc etc and much more etc with diagrams

from Motorola
http://mot-sps.com/motor/tutorial/ac.html
Motor Operation Principles
Motion Control Overview

Motion Control Tutorial
Motion Control Application Notes
Motion Control Products
Motion Control Development Tools

and just a few of their available pdf files

http://mot-sps.com/motor/appnote.html
AN2154 Low-Cost, 3-Phase, AC Motor Control System with Power Factor Correction Based on MC68HC908MR32
AN1919 Design of Indirect Power Factor Correction Using DSP56F80X
AN1916 3-phase BLDC Motor Control with Hall Sensors using DSP 56F80x
AN1913 3-phase BLDC Motor Control with Sensorless Back-EMF ADC Zero Crossing Detection using DSP 56F80x
AN1911 3-Phase AC Motor Control with V/Hz Speed Open Loop Using DSP56F80X
AN1910 3-Phase AC Motor Control with V/Hz Speed Closed Loop Using the DSP56F80X
AN1858 Sensorless Brushless dc Motor using the MC68HC908MR32 Embedded Motion Control Development System

[Napier]

Astro, I think do not take your point.
http://www.worldservo.com/html/arc.htm is a painfully verbose explanation about why this manufacturer's packaging choices for an AC servo drive are better for every application than their competitors, but says nothing at all about whether the commutation logic is self-teaching. Because of the number of times this page refers to phases etc, it comes up early in any reasonable web search on the question - I read it before posting my quesiton here.
http://mot-sps.com/motor/tutorial/ac.html and
http://mot-sps.com/motor/appnote.html are not even about servomotors per se, and the first one is limited specifically to induction motors that do not even have salient poles.
What answer do you think these sites is giving, that the drives are self correcting, or not? They just look like three wordy sites about motors, to me.